Insulating amide-imide polymeric magnetic wire coating composition



' U.S."Cl. 26031.2

ABSTRACTOF THE DISCLOSURE The thermoplastic flow, burnout, and smoothness of an amide-.imide polymeric coating of a magnetic wire is substantially improved by the addition of benzyl benzoate and/ or 1,4 butanediol in the initial coating composition.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to magnet wire coating composition and the resultant magnet wire. More particularly, it relates tothe use of at least one of the following additives in an amide-imide magnet wire coating composition:

benzyl benzoate and HOCH CH CH CH OH 1,4 butanediol Description of the prior art Amide-imide polymeric coating composition has been used for the manufacturing of an all-purpose magnet wire. Heretofore, acetanilide has been used as an additive to the solvent system of the amide-imide polymeric coating composition to improve the smoothness, thermoplastic .fiow' temperature, and the burnout characteristics of the "resultant insulationicoati'ng of the magnet wire. Acetanilide is a' crystalline substance having a boiling point at 302 C. and is soluble in N-methyl pyrrolidone or other f solvents for the amide-imide polymer.

In the manufacturing of amide-imide insulated magnet wire, the solvent of the coating composition is generally recovered by condensing the evaporated solvent. The pres ence of acetanilide in the solvent system, however, renders its recovery ineffective and oftentimes impossible. The

failure is caused by the recrystallization of acetanilide in the condenser. The'recry'stallized acetanilide coats on the pipes in the condenser and gradually plugs up the gaseous passages after two to three hours.

SUMMARY OF THE INVENTION I have now found that the use of acetanilide can be eliminated without sacrificing the physical characteristics of the resultant amide-imide polymeric coating of the magnet wire. The invention is based on thediscovery that at least one of the following additives, when it is used in combination with the existing amide-inside polymeric coat-' ing composition,substantially improves the smoothness, burnout characteristics and thermoplastic flow temperature of the resultant coating without the use of an acetanilide additives.v

Broadly stated, the magnet wire coating composition of this invention comprises (a) an amide-imide polymer, (b) a solvent system for the polymer, and (c) up to 15% by weight of .1,4-butanetliol and up to 30% by weight of United States Patent O benzyl benzoate. The composition has about 5%35% by weight of polymeric solids. The magnet wire coated with this composition has excellent physical properties and particularly the surface smoothness, thermoplastic flow temperature, and burnout resistance.

DESCRIPTION OF THE PREFERRED EMBODIMENT The polyamide-imide wire enamel suitable for the preparation of the magnet wire coating composition of the present invention includes solutions of polymers containing both amide and imide linkages and repeating units of wherein R is a residue of an organic diamine.

The polyamide-imide may be prepared by copolymerization of an acyl halide derivative of trimellitic anhydride (1,2,4-benzene tricarboxylic acid anhydride) and an aromatic primary diamine. The polymeric products may have the following structure:

wherein R is the aromatic nucleus of the starting diamine, H HRNH The linking groups are probably predominantly amido although some may be imido. The polymeric structure may also contain free carboxyl groups which are capable of further reaction. When the enamel is further reacted, for example, in the manufacture of the magnet wire the above-stated reaction products (A) and (B) are to form polymer conforming to the structure of The free carboxyl groups initially present in the polymeric structure are to a substantial extent converted to imide groups by condensation with available amide groups.

The acyl halide derivatives of trimellitic anhydride that are suitable for preparing the aforementioned polyamideimide polymer have at least one acyl halide group in the 4-ring position. They include, for example, 4-acid chloride, 1,4 and 2,4-diacid chloride (with an ester in the remaining position) and 1,2,4-triacid chloride. The bromides and other reactive halide derivatives are also suitable.

The aromatic diamine that may be used for preparing polyamide-imide enamel preferably have one or more aromatic rings and two primary amino groups. The aromatic diamines having more than one aromatic ring may amide-polyimide enamel used. In general, the presence of even a trace amount of one of these two additives will provide beneficial results. I found as much as 15% by weight of 1,4 butanediol and up to about 30% by weight of benzyl benzoate may be used in preparing the coating composition of this invention.

The additives preferably are added into the coatingcomposition during the preparation of the amide-imide polymer in a solvent. The resultant composition may be adjusted for viscosity and other additives, such as dicyandiamide and triphenyl phosphite, may also be added. The addition of acetanilide, however, is no longer required.

Further to illustrate this invention specifiic examples are described hereinbelow. In these examples, the amideimide polymer, unless otherwise specified, was prepared by reacting trimellitic anhydride and p,p methylene-bis- (aniline) in N-methyl-pyrrolidone and dimethyl octamide. The enamel containing 20%28% solids was further diluted with WES oil (a semi-refined coal tar distillate having a specific gravity of 0930-0950 and which distills 95% to not above 235 C.) to a suitable viscosity for smooth application.

The testing of the wire in accordance with the present invention which gave the results illustrated below was performed according to standard testing procedures which are well described in publications of the American Society for Testing Materials, the American Standard Association, the American Institute of Electrical Engineers and military specifications.

EXAMPLE I 30% by weight of benzyl benzoate was added into and mixed with an amide-imide polymeric coating composition containing 0.3% by weight of dicyandiamide and 0.3% by weight of triphenyl phosphite. After thoroughly mixing, the coating composition was used in the manufacturing of magnet wires using a vertical oven at the feed rate of 18 feet per minute at three different baking temperatures, 400 0., 430 C., and 460 C. A total of six coats were applied. The results are tabulated hereinbelow:

In the coating process, it wasnotedbenzyl benzoate,

which boils at 324 C., was condensed as liquid and did not hinder the recovery of the solvent. A portion of benzyl benzoate was recovered.

EXAMPLE 11-" The amide-imide polymeric enamel which contained 28% solids in a solvent consisting of N-methyl pyrrolidone and 25% WES oil, having a viscosity of 70 poises, was used to prepare magnet wires of 18'AWG copper conductors on a horizontal 12 -ft. coating unit using a typical formulation as follows:

. i i .Percent by weight Amide-imide polymer plus'about 0.5 triphenyl phosphite and 0.3 dicyandiamide 70 Benzyl benzoate 25 1,4 butanediol v5 Build 1.9 mil.

Coating surface Smooth.

ITC scrape 996 Ave.

G.E. scrape Snap +5X OK.

20% flex 3X, 2X OK. Heat shock 20% 3X 2X OK. 42% elongation No lift, no cracks. Thermoplastic flow 400 0., 402 C.

Progressive burnout to 44 amps. 736 sec.

Maximum speed on the 12 ft. horizontal oven was 30 feet per minute.

EXAMPLE III Using the amide-imide polymer described in Example 11, the following coating composition was used to coat 18 AWG copper wire on a 12 ft. horizontal oven at 20 f.p.m.:

Percent by weight Amide-imide polymer 70.0 Benzoyl benzoate 26.2 1.4 butanediol 3.8 Triphenyl phosphite 0.5 Dicyandiamide 0.3

The resultant magnet wires prepared at different oven temperatures are tabulated hereinbelow:

Thermoplastic flow Burnout to 44 amps TABLE II Test 390 0 405 0. 420 0 Build 2.0 1.9 1.8. Coating surface-.-. Smooth Smooth Full snap +3X OK nap +3X OK 20% elongation 3X, 2X, LX 0K... 3X, 2X, 1X OK. Heat shock.... 3X, 2X OK.-- Same 20% 3X, 2X, 1X OK." ITO scrape 1,000 ave 970 ave... 996 ave. G.E. scrape 100+ ave 100+ ave. 100+ ave 40% elongation.-. No lift, no erkcks Solvent resistance. OK OK K.

.. 734.8 sec.

EXAMPLE IV zontal unit. The following represents results on the mag- Using the Same amidedmide polymer of Example H net wire prepared at three different temperatures:

TABLE V Test 390 0. 405 0. 420 C.

Speed Max. speed. 33 f.p.m. G.E. scrape 100+ ave 100+ ave. 1T0. Scrape..- 940 ave.. 1,207 ave. Snap Fu1l+4X OK" 4X 3X OK. 20% elongation 3X, 2X, 1X, Wrap, OK-. 3X, 2X, 1X OK.- 3X, 2X, 1X 0K. Heat shock at 150 for 1 hr 3X, 2X,1X OK 3X, 2X,1X 0K..... 3X, 2X,1X OK. 20% elongation N o bare copper, no lift, no cracks N o hare copper, no lift, no cracks No bare copper, no lift, no cracks. DMAC OK, no cracks.

41% elongation to break. 42% elongation to break 46% elongation to break Solvent test DMAC OK, no cracks.

Burnout 594-5 sec., 743.5 sec. -44 amp 758.9 sec. at 44 amps. Build 2.3 mils 2.2 mils 2.211111 the following coating composition was used to coat 18 Iclaim: AWG copper wire on a 12 ft. horizontal oven at 17 f.p.m.: 1. A magnet wire coating composition comprising (a) Percent by weight 20 an amide-imide polymer, (b) a solvent system for said Amide imide P y 75 0 polymer, and (c) at least one of the following additives: Benzyl benzoate 0 (1) trace amounts up to by Weight of the com- 1 4 butanediol u 15 0 position of 1,4 butanediol, and (2) trace amounts up u to by weight of the composition of benzyl benzoate, Six coats were applied to the copper wires. The magnet and said composition containing about 5 %3 y wire prepared at different operational conditions is tabu- We1ght of sollds. lat d h inb l 2. A magnet wire coating composition of claim 1 TABLE III Test 390 0. 405 0. 420 C.

Coating surface. Smooth- Slightly sandy... Fairly smooth. Snap Full snap ITO scrape..- 920 mm... G.E. scrape 100+ 100+ 100+ 40% elongation Nolift, no cracks-.. N 0 lift, no cracks.- No hit,

no cracks. 20% snap 3X, 2X, 1X OK... 3X, 2X OK +3X, 2X OK. Heat shock All OK 20% 3X, 2X OK 3X, 2X 0K. Thermoplastic fl 370-390 C.

1 hr. at 150 0. Will run at 28 f.p.m. on 12 ft. horizontal.

EXAMPLE V wherein the composition contains both 1,4 butanediol and benzyl benzoate.

3. A magnet wire coating composition of claim 1 wherein the composition contains only benzyl benzoate.

The following coating composition was used to coat 18 AWG copper wire on a 12 ft. vertical dieless unit:

Pfir t 4. A magnet wire coating composition of claim 1 Arnide-imide polymer 9 wherein the composition contains only 1,4 butanediol. 1,4 butanediol 5 5. A magnet wire coating composition of claim 1 The following results were Obtained: wherein the composition contains in addition 0.1% to 0.5% by weight of triphenylphosphite and 0.1% to 0.5%

TABLE IV by weight of dicyandiamide. I Test A B 6. A magnet wire comprising a conductor and coated Temperature C 0 Q thereon a cured polymeric layer of a coating composition B ilt 1.4 mil 5C0atS 1.4 accordlng to claim 1.

th Smooth 7. A magnet wire according to claim 6 wherein the coating composition contains 1,4 butanediol and benzyl benzoate.

8. A magnet wire of claim 6 wherein the coating composition contains 1,4 butanediol.

9. A magnet wire of claim 6 wherein the coating composition contains benzyl benzoate. 10. A magnet wire of claim 6 wherein the coating XA PL V composition contains 0.1%0.5% by weight of triphenyl- Amidedmide polymer prepared with the Solvent was phosphite and 0.1%-0.5% by weight of dicyandiamide. used for preparing the coating composition of the invention. The composition was as follows: References Cited Percent by weight UNITED STATES PATENTS Amide-imide polymer (solids) 28.0 3,320,202 /1967 Bolton et al. 260-302 N-methyl pyrrolidone 33.6 3,355,427 11/1967 Loncrini 260-334 WES oil 113 3,364,166 1/1 8 BaIiiO 26030.2 Benzoyl benzoate 22,3 3,440,203 4/1969 Boldebllck et al. 260-33.4

513532 13}. 03 ALLAN LIEBERMAN, Primary Examiner Tnphenylphosphite 0.5 US. Cl. XIR- The viscosity of the composition was 55 poises at 25 C. The 18 AWG copper wire was coated on a 12 ft. hori- 260.402 117 232 

